1. Field of the Invention
The invention relates to internal combustion engines, particularly a fuel injection nozzle for delivering fuel to the fuel combustion chamber of an engine.
2. Background Art
A fuel injection pump for a conventional internal combustion engine, such as a diesel engine, comprises a pump plunger or piston situated in a pump cylinder to define a high pressure pumping chamber. The plunger is driven with a pumping stroke by an engine rocker arm for intake and exhaust valves for the engine or by some other camshaft driven member. The stroking of the plunger thus is related directly to engine speed.
A low-pressure fuel pump supplies the pumping chamber with fuel. A fuel control valve having open and closed states is located in a fluid supply passage between the outlet side of the low-pressure fuel pump and the pumping chamber for the fuel injection pump. An electronic engine controller repeatedly and sequentially changes the state of the fuel control valve from a flow open state to a flow closed state during a predetermined cycle time so that an initial pilot pulse of fuel is delivered to an injection nozzle in advance of the delivery of the full injection pulse. The presence of the pilot pulse contributes to more efficient burning of the fuel in the combustion chamber of the engine, thereby reducing undesirable exhaust gas emissions and increasing the combustion temperature of the fuel. This improves the combustion efficiency and promotes complete burning of the fuel delivered by the full injection pulse.
In a conventional fuel injection system, the controller lacks the ability to establish a definitive pilot pulse that precedes the development of the full injection pulse. This is due, in part, to an inherent delay in the development of injection pressure following a so-called ON command to the control valve by the controller. It is due also to the inability of the control valve to terminate a fuel pressure buildup at the injection nozzle following a so-called OFF command by the controller to close the control valve.
In the control of the fuel delivery in response to the ON/OFF commands of the controller, the pilot fuel delivery pulse blends into the full injection pulse so that fuel delivery through the injection nozzle occurs during a single, extended fuel injection event. This imprecision in the establishment of a pilot pulse in advance of the full injection cycle makes controlled fuel metering difficult. Excess fuel is delivered during each injection cycle, which may result in instability in combustion in the engine combustion chamber and excess undesirable exhaust gas emissions.
The lack of precision in the delivery of fuel pulses in conventional fuel injection systems makes it more difficult to achieve constant volume combustion of the fuel/air mixture in the combustion chamber. Complete combustion should occur with a minimum travel of the piston. This feature is difficult to achieve if the fuel pulses are blended, during an extended injection event, with no controlled interval between the pulses. Constant volume combustion will contribute to more efficient fuel economy.
It is an objective of the invention to overcome imprecision in the delivery of fuel pulses by a fuel injection nozzle in a fuel injection engine by providing a distinct, controlled pilot pulse in advance of the full fuel injection pulse. This creates a controlled interval between the two pulses so that more efficient fuel burning in the combustion chamber can be achieved. The invention includes a fuel nozzle at the fuel delivery side of a pumping chamber for a fuel injector that is driven by an engine rocker arm or some other engine-driven element. The fuel injector has a plunger that reciprocates in a fuel injection cylinder. During the pumping stroke of the plunger, fuel is transmitted under high pressure to a fuel spray orifice in the nozzle. The orifice is controlled by a needle valve that responds to a pressure buildup at the orifice.
The needle valve is moved into sealing engagement with the nozzle so that the needle valve tip can control the opening and closing of the orifice. The needle valve is biased by a valve return spring toward the orifice closing position and is biased by fuel pressure against an opposing force of the spring at a predetermined fuel pressure level developed by the plunger as it is stroked in the pumping chamber.
A damper plate is situated between the needle valve return spring and the tip of the needle valve. The needle valve cooperates with the damping plate to define an accumulator with an accumulator chamber. As the needle valve is stroked to its open position, the accumulator displaces fuel through an accumulator leak path formed in the damping plate. The leak path is defined in part by a damper pin, which cooperates with the damping plate to define a restricted flow path for the fuel as the fuel is displaced from the accumulator chamber by the needle valve. This produces a damping effect, which decreases the rate the needle valve opens. The decreased opening rate prevents the needle valve from achieving a fully opened state during the development of a short pilot injection pulse.
The damper plate and the damping pin control the speed at which the needle valve moves from the orifice closing position to the fully open position. The damping feature acts in synchronism with the ON/OFF cycles delivered by the controller to the fuel control valve so that an OFF command for the fuel control valve is established prior to the development of the peak value for the pilot pulse. Further, the ON command for the fuel valve occurs after the pilot pressure has decreased to approximately the threshold value that normally exists when the needle valve assumes an orifice open position. The outset of the full injection pulse occurs following a calibrated delay from the instant the ON command is delivered to the fuel control valve so that the development of the fuel injection pulse occurs with a calibrated, controlled delay following the peak pilot pulse pressure. In this way, a blending of the two pulses into a single, long injection event is avoided.
The nozzle has a nozzle tip portion in which the fuel spray orifice is formed. The needle valve is in the nozzle tip portion.
A first end of the needle valve engages the nozzle tip portion and closes the orifice when the needle valve assumes a first position.
A fuel flow passage is defined by a clearance between the damper plate and the damper pin. This is a calibrated clearance, which provides a flow restriction. The damper pin extends into the accumulator chamber, whereby fluid displaced from the accumulator chamber by the needle valve, as the needle valve is shifted under pressure toward the damper plate, passes through the flow restriction.
A compression spring in the nozzle body acts on the damper pin, thereby opposing movement of the needle valve under a differential pressure acting on the needle valve. The compression spring engages a movable spring seat, which is engaged by the damper pin. In accordance with one feature of the invention, the spring chamber in the nozzle body is in restricted communication through a flow control orifice with a high pressure fuel delivery passage extending to the injection nozzle. The pumping stroke of the plunger increases the pressure in the fuel delivery passage, as explained. This, in turn, results in a delayed pressure buildup in the spring chamber because of the restricted flow passage between the high pressure fuel delivery passage for the needle valve and the chamber occupied by the spring. The pressure in the spring chamber creates a hydraulic force that complements the force of the spring acting on the damper pin. This causes the forces acting on the needle valve to be more closely balanced, thereby permitting the use of a reduced stress spring or a reduced spring rate.
The pressure in the spring cage trails the injection pressure during the injection cycle because of the flow metering effect of the control orifice between the high pressure fuel delivery passage and the spring chamber. The resulting pressure difference between the pressure in the fuel delivery passage for the needle valve and the pressure in the spring chamber does not interfere with the opening of the valve. The valve will pop open when a threshold pressure is achieved to create a pressure differential force to oppose the spring force. The pressure differential will, however, provide a cleaner and crisper end of the injection cycle. This potentially lowers the undesirable emissions from the engine and improves engine operating efficiency.
Because of the presence of fuel pressure acting on the damper pin, the closing of the needle valve occurs much more rapidly relative to the rate of closing of the needle valve if the damper pin is subjected solely to spring force.
Any leakage of fuel under pressure past the damper pin can be drained through a drain hole located at an intermediate position in the damper pin opening. The drain hole extends to a low pressure drain passage.
The response time of the needle valve to an OFF command of the control valve is greatly improved, thereby providing a more definitive termination of a pilot pulse before the initiation of a main injection pulse.